blob: 874ff0f635144acc4cc405723feff3203674e8cb (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
|
/*
* $Id$
*
* ***** BEGIN LGPL LICENSE BLOCK *****
*
* Copyright 2009 Jörg Hermann Müller
*
* This file is part of AudaSpace.
*
* AudaSpace is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* AudaSpace is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with AudaSpace. If not, see <http://www.gnu.org/licenses/>.
*
* ***** END LGPL LICENSE BLOCK *****
*/
#include "AUD_ButterworthFactory.h"
#include "AUD_IIRFilterReader.h"
#include <cmath>
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
#define BWPB41 0.76536686473
#define BWPB42 1.84775906502
AUD_ButterworthFactory::AUD_ButterworthFactory(AUD_IFactory* factory,
float frequency) :
AUD_EffectFactory(factory),
m_frequency(frequency)
{
}
AUD_IReader* AUD_ButterworthFactory::createReader() const
{
AUD_IReader* reader = getReader();
// calculate coefficients
float omega = 2 * tan(m_frequency * M_PI / reader->getSpecs().rate);
float o2 = omega * omega;
float o4 = o2 * o2;
float x1 = o2 + 2 * BWPB41 * omega + 4;
float x2 = o2 + 2 * BWPB42 * omega + 4;
float y1 = o2 - 2 * BWPB41 * omega + 4;
float y2 = o2 - 2 * BWPB42 * omega + 4;
float o228 = 2 * o2 - 8;
float norm = x1 * x2;
std::vector<float> a, b;
a.push_back(1);
a.push_back((x1 + x2) * o228 / norm);
a.push_back((x1 * y2 + x2 * y1 + o228 * o228) / norm);
a.push_back((y1 + y2) * o228 / norm);
a.push_back(y1 * y2 / norm);
b.push_back(o4 / norm);
b.push_back(4 * o4 / norm);
b.push_back(6 * o4 / norm);
b.push_back(b[1]);
b.push_back(b[0]);
return new AUD_IIRFilterReader(reader, b, a);
}
|
